Since the invention brings about similar advantageous effects on both a semiconductor device using metal oxide ferroelectrics (referred to hereinafter merely as ferroelectrics) and a semiconductor device using metal oxide dielectrics (referred to hereinafter merely as high dielectrics), description given hereinafter will center on the semiconductor device using ferroelectrics.
Attention has been focused on a ferroelectrics memory as the semiconductor device using the ferroelectrics. Research and development on a memory using the ferroelectrics have since been very active because it is a nonvolatile memory wherein the contents of the memory are not erased taking advantage of a polarization phenomenon of the ferroelectrics even if power supply is cut off while random access can be made thereto.
For a ferroelectric film, there has since been in commercial application material using a layered bismuth perovskite which is a layered bismuth (Bi) compound: SrBi2Ta2O9 (a group of series of compounds including those having a composition which is a variation to this composition, and those with such an additive as represented by niobium (Nb) added thereto are referred to hereinafter as SBT), and a lead zirconate titanate: Pb(Zr1-xTix)O3 (a group of series of compounds including those having a composition which is a variation to this composition, and those with such an additive as lanthanum (La), calcium (Ca), and so forth, added thereto are referred to hereinafter as PZT).
Further, ferroelectric materials in a study stage include bismuth titanate with lanthanum added thereto, called BLT, those ferroelectric materials described in the foregoing with other dielectric material in solid solution form, added thereto, and so forth, and those ferroelectric materials described above have one thing in common in that heat treatment needs to be applied thereto in an oxygen atmosphere for exhibiting ferroelectricity as oxide crystals in respective cases, so that all those ferroelectric materials can gain equivalent advantageous effects by virtue of the present invention. Hence, the case of using a ferroelectric film, in particular, a SBT film will be described in detail hereinafter.
As described above, the ferroelectrics such as SBT, and so forth are all metal oxide crystals, and require heat treatment at a high temperature in a range of 600 to 800° C. at the time of crystallizing those materials, and in order to heal process damage incurred during sputtering, etching, etc., in the back-end steps of manufacturing. In addition, the heat treatment is applied in an oxygen atmosphere in most cases, so that in the case of a semiconductor device fabricated prior to the formation of a ferroelectric capacitor, comprising wiring made of tungsten (W) etc, and a contactor structure, these constituents are easily oxidized in the oxygen atmosphere, and upon oxidation, conductivity thereof is lost, thereby necessitating some countermeasure for prevention of oxidation.
Meanwhile, in the case of manufacturing a semiconductor device by use of photolithographic techniques, there is the need of a pattern yet to be formed being superposed on (aligned with) a pattern already formed on an underlying layer with precision. Accordingly, aside from a device pattern, alignment mark patterns intended solely for executing such alignment with precision are simultaneously formed.
Principal alignment marks fall into three broad categories, that is, a mark (search mark) for rough alignment, to be read by an optical aligner when subjecting a resist (photosensitive agent) to exposure by use of the optical aligner, a mark (fine mark) for precision alignment, and an alignment measurement mark for detection of misalignment by use of an alignment measuring instrument after exposure and development. These alignment marks have no direct bearing on the function of a semiconductor device, but are indispensable in the manufacturing the semiconductor device.
As described above, the principal alignment marks have three varieties, however, since a problem with each of the three varieties and a countermeasure for solving the problem are common to all of them, the alignment measurement mark will be described hereinafter. FIG. 7 shows a typical construction of alignment measurement marks formed by a conventional method, FIG. 7A is a schematic plan view of the alignment measurement marks, FIG. 7B a sectional view thereof, taken along line a—a of an out-box in FIG. 7A, and FIG. 7C a sectional view thereof, taken along line b—b of an in-box in FIG. 7A. The alignment measurement marks are made up of two rectangular patterns constituting the out-box and the inbox, respectively. For example, in the case of aligning a pattern layer 1 with a pattern layer 2, an out-box 400 is first formed with the pattern layer 1 to serve as an underlying layer against the pattern layer 2, and subsequently, an in-box 410 is formed in the step of applying photolithographic techniques to the pattern layer 2.
Conversely, in the case of forming the in-box with the pattern layer 1, the out-box is formed with the pattern layer 2. The in-box (or the out-box) formed with the pattern layer 2 is made up of a resist. The alignment measurement marks made up of the out-box and the in-box are measured by the alignment measuring instrument, thereby detecting an amount of discrepancy in alignment of the pattern layer 2 relative to the pattern layer 1. If the amount of the discrepancy is greater than a specified value, the resist is removed in its entirety, and a pattern 2 is again formed with the use of an alignment correction value as obtained. After the photolithographic step, a resist pattern of the in-box (or the out-box) is subjected to etching except the step of ion implantation and is left out on a wafer. Accordingly, it is indispensable from a manufacturing point of view to suppress oxidation and exfoliation of a mark part to a minimum in back-end steps.
FIG. 7 is view corresponding to a case where the out-box is formed when forming a BMD (Buried Metal on Diffusion Layer) contactor, and thereafter, the in-box is formed in succeeding steps. After forming a groove in an interlayer insulating film 401 in a BMD contactor hole etching step, a metal film 402, made of tungsten (W) etc, is formed by the CVD method, and thereafter, a CMP (Chemical Mechanical Polishing) is applied thereto or the entire surface thereof is etched back. The figure shows a state where residue of tungsten (W) remains in the form of a sidewall at respective edges of the out-box. Subsequently, an interlayer insulating film 403 is deposited, and the interlayer insulating film 403 is normally of a layered structure including not only a silicon oxide film but also a silicon nitride film, and so forth, in order to prevent oxidation of underlying tungsten (W).
Further, after applying a photolithographic step to the in-box, etching is applied to the interlayer insulating film 403 in a contactor hole etching step, and thereafter, a metal film 404, made of tungsten (W) etc, is formed by the CVD method, subsequently applying the CMP (Chemical Mechanical Polishing) thereto, or etching back the entire surface thereof. A portion of the metal film 404, which is residue of tungsten (W), remains at respective edges and the bottom of the in-box. Since there exists a stepped part on a portion of the interlayer insulating film 403 as well, on top of the out-box, there is a possibility of portions of the metal film 404 also remaining therein at this point in time.
Accordingly, remaining portions of the metal film 404 easily undergo intense oxidation during heat treatment in an oxygen atmosphere, and so forth, applied for crystallization of the ferroelectrics in back-end steps. Remaining portions of the metal film 402 do not have sufficient oxidation resistance either. Because of difference in level of the interlayer insulating film due to the formation of the out-box, the silicon nitride film in regions where tungsten residue remains does not have a sufficient coating, and in addition, the silicon oxide film of the interlayer insulating film allows oxygen to be permeated (diffused), so that, as shown in FIG. 8, tungsten (W) is seen intensely oxidized due to heat treatment in an oxygen atmosphere, accompanying the formation of the ferroelectrics. Occurrence of such intense oxidation as causing distortion of the shape of the marks will cause very serious problems from the viewpoint of manufacturing a semiconductor device, such as exfoliation, generation of particles in the back-end steps of manufacturing, and so forth.